1. Field of the Invention
The present invention relates to a metallic hollow golf club head and, more particularly, to a golf club head in which a face plate is welded to an opening formed in a face part.
2. Description of Related Art
As a conventional metallic hollow golf club head in which a face plate is welded, a golf club head as shown in FIG. 7 has been known. In this golf club head, a substantially rectangular opening 20 is formed in a face part 2 of a metallic head body 1 having a hollow part 10 therein, and a face plate 30 having a shape matching the opening 20 is laser welded to a receiving part 2B formed at the periphery of the opening 20. The head body 1 includes a crown part 3, a sole part 4, and a hosel 5 in addition to the face part 2, and has a toe 6 and a heel 7. In this conventional examples, the welding strength is improved, and therefore damage is less likely to occur (Japanese Unexamined Patent Application Publication No. 2004-65853 (p.4, FIG. 1)).
Also, as a golf club head in which the whole of face part is a member separate from the head body and this face part is welded to the head body, there has been known a golf club head in which the face part is deflected when the ball is hit by decreasing the thickness of the face part, thereby increasing carry. Due to the shape of the head body, such a face part is formed so that the length in the right and left direction (the toe-heel direction) is greater than the length in the up and down direction (the top-sole direction). Therefore, the deflection of the face part when the ball is hit is greater in the right and left direction than in the up and down direction, and the slope toward the center position at which the deflection is greatest is gentler in the right and left direction than in the up and down direction of the face. For this reason, when the ball is hit, the ball is not compressed while the ball cross section perpendicular to the hit direction (the ball compressing direction) is maintained in a circular shape. Uneven compression causes distortion of the circular cross-sectional shape, which makes it difficult to control the direction that the ball flies.
As a golf club head which, by preventing the occurrence of anisotropy, compresses a ball into an even shape and increases the rebounding force when the ball is hit, there has been known a golf club head in which an opening having almost the same lengths in the up and down direction and the right and left direction is formed in the face part, and a face plate having the same shape as that of the opening is welded to the opening (Japanese Unexamined Patent Application Publication No. 2003-265656 (p.2, FIG. 1)).
The conventional face plate has been developed assuming that a golfer hits a ball at the center of a face plate or the periphery thereof, that is, the sweet spot and therefore the conventional face plate does not sufficiently accommodate variations in hit points of general amateur golfers. The conventional example in Japanese Unexamined Patent Application Publication No. 2003-265656 has been invented from the viewpoints described below. The material of head is changed from stainless steel to titanium alloy in response to recent tendency. Along with the increase in size of the head, titanium alloy has a high strength in comparison with its low Young's modulus, which is about 60% of that of stainless steel, and therefore the thickness of the face surface is decreased to deflect the face surface when the ball is hit, by which the initial velocity (delivery velocity) of the ball is increased. However, when a ball is hit at a portion deviating from the sweet spot, especially at the face part such as a toe upper portion or a heel lower portion other than the substantially square-shaped face plate, the carry decreases extremely.